As with anything like this, the more sensitive you make it, the more you might have to deal with false positives.

I can only imagine someone going around bumping into people at the airport making sure they all smell like something which will trigger something like this.

It wouldn't be anything more disruptive than suddenly loads of people in the airport get checked for bombs, but I bet you could terribly mess up an airport if you suddenly had a handful of people testing positive.

Of course, to be going around doing this you'd need to smell of bomb residue and probably be seen on surveillance cameras doing it. But for all I know some common household chemicals could cause this now.

Of course, to be going around doing this you'd need to smell of bomb residue and probably be seen on surveillance cameras doing it.

That doesn't matter. What matters is that you can deposit a chemical on a large number of others who have a high probability of going quickly to an airport security check. You never need to go near the sensors yourself.

One easy exploit is to rig a aerosol dispersal into a car's exhaust, then drive through a departures drop-off area a few times. Alternatively, contaminate the air around a rental car return. If the airport is one of those with significant public areas outside the secure area, a purse with an occasionally-puffing atomizer will be practically unnoticeable. Better yet, disguise the purse-riding atomizer as a wallet, and confess to coming to the airport in the middle of a pickpocketing spree. Bonus points if the pickpocketing is also staged for the benefit of cameras.

Taking another easy route, we could assume that contact's necessary to spread the scent to a person. That's also easy enough to accomplish. How many countertops, queue barrier posts, and restroom faucets are in an airport? With a small team of pre-contaminated guests with many complaints and small bladders, a barely-noticeable compound can be spread to hundreds of unsuspecting participants easily.